The overall objective of this neuroendocrine project is to elucidate the role of hypothalamic biogenic amines and hypophysiotropic hormones in the regulation of luteinizing hormone (LH) and prolactin release during several different reproductive states in the rat. With this goal in mind, information will be sought on the relationship of the activity of biogenic amine-containing neurons in the hypothalamus (as revealed by the amine content and/or activity of the biosynthetic enzymes), to the concentration of hypophysiotropic hormones and the pattern of LH and prolactin secretion. Several physiologic states have been selected for investigation, which include the following: estrous cycle, pregnancy and pseudopregnancy, lactation, ovariectomy, and gonadal steroid and pituitary hormone feedback. These were included because the pattern of LH and prolacting secretion is either directly or reciprocally related and during these states LH and prolactin are regulated by either hormonal or neural input. The site(s) in the hypothalamus where changes in biogenic amines and hypophysiotropic hormones may occur will be determined in addition to analyzing the whole hypothalamus. This is necessary because large changes in one area of the hypothalamus may be masked if only whole hypothalami are analyzed. Determination of circulating levels of LH and prolactin and hypothalamic levels of LH-RH will be done by radioimmunoassay. Activity of biosynthetic enzymes will be done in vitro using radioactive substrates and biogenic amine levels will be determined using isotropic enzymatic microassays. These experiments will be done largely in unanesthetized, unrestrained animals, and will serve as the basis for understanding what role hypothalamic biogenic amines play in directing the response of LH and prolactin to physiological stimuli associated with reproduction.